Previously, curable compositions, cured by active energy rays such as ultraviolet rays and electron rays or by heat, have been applied in practice for various applications of such as paint for plastic, paper, woodwork and inorganic materials; adhesives, printing ink, printed circuit boards and electrical insulation. In recent years, desired have been further improvements of weather-proofing and adhesion, of printing ink, paint and adhesives among them. Further, there is an ultraviolet ray curable inkjet ink which cures by ultraviolet rays as inkjet ink employing these active ray curable compositions. An inkjet recording method employing the ultraviolet curable ink has become noted these recent years with respect to relatively low odor, rapid drying and the capability of recording on a recording medium exhibiting no ink absorbability, and disclosed is such an ultraviolet curable inkjet ink (for example, please refer to patent documents 1 and 2). In this application, inkjet ink is required to have a low viscosity and to form a stronger and more flexible layer. Provision of plasticity by addition of a plastisizer in inkjet ink is disclosed (for example, please refer to patent document 3). However, these plasticizers are for fusing type ink and there is no description for ultraviolet curable inkjet ink.
Further, when utilizing such ink, a problem is that the curing sensitivity tending to vary depending on the type of recording materials and printing environment.
Since ink utilizing a radical polymerizing compound exhibits an oxygen inhibition effect, curing is inhibited and is especially caused when an ink liquid drop quantity is low. Further, ink utilizing a cationic polymerizing compound (for example, refer to patent documents 4-7) exhibits no oxygen inhibition effect, however, it is easily affected by water content (humidity) at the molecular level.    Patent document 1: JP-A 6-200204 (hereinafter, JP-A refers to Unexamined Japanese Patent Application Publication)    Patent document 2: Japanese Translated PCT Patent Publication 2000-504778    Patent-document 3: JP-A 8-3493    Patent document 4: JP-A 2001-220526    Patent document 5: JP-A 2002-188025    Patent document 6: JP-A 2002-317139    Patent document 7: JP-A 2003-55449